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Everyone on Earth is your cousin (2015)

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Re: Everyone on Earth is your cousin (2015)

#41

Post by lordnacho »

fastball wrote: post #28
tzs wrote: post #7

There are a few particularly interesting points when you go back up your ancestor tree. First, there is a point where some ancestor of yours is an ancestor of everyone else currently living (and so will also be an ancestor of everyone else to come). This is the "most recent common ancestor" point. Go farther back and you reach the "identical ancestors point" (also known as the "all common ancestors point" or the "gen…

Maybe I'm stupid but I'm not sure I understand the difference between most recent common ancestor and the identical ancestors point. Can someone explain differently?

MRCA: Take every current person's family tree, who is the most recent person who is in all of them? This doesn't mean there was only one ancestor around at the time, though if all life came from the same cell that is of course true if you go back that far.

IAP: For any given time X, every person at time X is either an ancestor of all current people, or none. Take everyone's family tree, and since it can't be size 2^x generations back, the overlaps eventually mean that all those people at time X who have a current descendent actually have everyone alive currently as their descendant, and everyone else at time X is the ancestor of nobody currently alive.

Re: Everyone on Earth is your cousin (2015)

#42

Post by lordnacho »

irrational wrote: post #25
mettamage wrote: post #13

Earlier quoted context omitted.

Another thing I find interesting is that your family right now are the most closest humans related to you. When you go back in time or forward in time, the relatedness dilutes.

Even then, you and your sibling could, statistically, share zero genes (you each get 50% from each parent and it is possible you each got a different 50%). Your own parents and children are the closest relatives you have since you are guaranteed to have 50% of your parent’s genes and same with your children.

Identical twins are truly special in that sense.

Re: Everyone on Earth is your cousin (2015)

#43

Post by [deleted] »

fastball wrote: post #28
tzs wrote: post #7

There are a few particularly interesting points when you go back up your ancestor tree. First, there is a point where some ancestor of yours is an ancestor of everyone else currently living (and so will also be an ancestor of everyone else to come). This is the "most recent common ancestor" point. Go farther back and you reach the "identical ancestors point" (also known as the "all common ancestors point" or the "gen…

Maybe I'm stupid but I'm not sure I understand the difference between most recent common ancestor and the identical ancestors point. Can someone explain differently?

[deleted]

Re: Everyone on Earth is your cousin (2015)

#44

Post by quietbritishjim »

fastball wrote: post #28
tzs wrote: post #7

There are a few particularly interesting points when you go back up your ancestor tree. First, there is a point where some ancestor of yours is an ancestor of everyone else currently living (and so will also be an ancestor of everyone else to come). This is the "most recent common ancestor" point. Go farther back and you reach the "identical ancestors point" (also known as the "all common ancestors point" or the "gen…

Maybe I'm stupid but I'm not sure I understand the difference between most recent common ancestor and the identical ancestors point. Can someone explain differently?

At any given moment in time, let n be the number of people who are an ancestor of everyone alive in 2021 (or 2022!).

Right now, n = 0 because there is nobody on earth that is the anscestor of everybody else.

If you go back far enough, you'll get n = 1. That's a single person that is an anscestor for everyone alive today. That's the most recent common anscestor. Other people then were anscestors to only some people alive today.

If you go back further, you'll get n = total number of people on the planet at the time. Everyone on earth is an anscestor of people alive today.

Except, wait, that's not true! There will always be some people alive who aren't anscestors to anyone alive today. Maybe they simply didn't get lucky at all in their lifetime, or were infertile. Maybe a collection of people only bred within a community (tribe, city, etc) which then got wiped out in a war. Maybe something more complex happened. So n=1 is possible, but n=everyone never happened.

So, totally ignore all the people who aren't anscestors to anyone in 2021, leaving only people that still have at least some anscestors today. Then n = 1 is (still) the most recent common anscestor. And the earlier date, n = everyone (that we care about) is the identical anscestors point.

Re: Everyone on Earth is your cousin (2015)

#45

Post by fastball »

quietbritishjim wrote: post #44
fastball wrote: post #28

Earlier quoted context omitted.

Maybe I'm stupid but I'm not sure I understand the difference between most recent common ancestor and the identical ancestors point. Can someone explain differently?

At any given moment in time, let n be the number of people who are an ancestor of everyone alive in 2021 (or 2022!). Right now, n = 0 because there is nobody on earth that is the anscestor of everybody else. If you go back far enough, you'll get n = 1. That's a single person that is an anscestor for everyone alive today. That's the most recent common anscestor. Other people then were anscestors to only some people al…

Ah makes sense, I think the use of present tense in the original explanation was throwing me for a loop.

Re: Everyone on Earth is your cousin (2015)

#46

Post by Borrible »

Your Highnesses, Dear Cousins, Peers.

Allow us to draw your attention to the state of intellectual exchange between our honorable houses, which we have enjoyed in the past.

https://nautil.us/issue/56/perspective/youre-descended-from-...

https://www.scientificamerican.com/article/humans-are-all-mo...

Discussed here: https://news.ycombinator.com/item?id=24686904

Re: Everyone on Earth is your cousin (2015)

#47

Post by kqr »

kingcharles wrote: post #29
Jensson wrote: post #17

Almost every country was very homogeneous just 50 years ago, so your family tree wont branch out like that normally. USA is a bit different since it is a nation of immigrants, but mostly people barely even left their villages historically.

Also, if you go back a few hundred years there were relatively so few people on the Earth. I bought First Wife a posey ring from 1600s England. I was interested to know just how many people were around then. It was about 5% of the current population. The world was empty.

Well. There were fewer people, yes, but they also moved around a lot more. It's only comparatively recently that we've gotten stuck in our places and social structures.

Re: Everyone on Earth is your cousin (2015)

#48

Post by plafl »

irrational wrote: post #25
mettamage wrote: post #13

Earlier quoted context omitted.

Another thing I find interesting is that your family right now are the most closest humans related to you. When you go back in time or forward in time, the relatedness dilutes.

Even then, you and your sibling could, statistically, share zero genes (you each get 50% from each parent and it is possible you each got a different 50%). Your own parents and children are the closest relatives you have since you are guaranteed to have 50% of your parent’s genes and same with your children.

> share zero genes

That would be impossible, unless one of you is some kind of bacteria. And even in that case I doubt it. According to Wikipedia[1] (yes, I invested some time to refute a random stranger on the internet, well, maybe a cousin) there is something like 0.1-0.4% of genetic variation between humans.

[1] https://en.wikipedia.org/wiki/Human_genetic_variation

Re: Everyone on Earth is your cousin (2015)

#49

Post by abc_lisper »

irrational wrote: post #40
abc_lisper wrote: post #33

Earlier quoted context omitted.

Not true. Australian aborigines split off 40k years ago. Now, if somehow we interbred with all of them, so that no pure aborigines are left, in a 100 years we move the line to a date that resembles what you suggest. We have to do that every remote tribe on earth. Or if for some reason they are killed.

Are you saying not true without even reading the studies, speaking from scientific knowledge, or speaking off the cuff?

I was wrong. Just checked Dawkins’ “ancestor tale”.

Re: Everyone on Earth is your cousin (2015)

#50

Post by dmurray »

kqr wrote: post #47
kingcharles wrote: post #29

Earlier quoted context omitted.

Also, if you go back a few hundred years there were relatively so few people on the Earth. I bought First Wife a posey ring from 1600s England. I was interested to know just how many people were around then. It was about 5% of the current population. The world was empty.

Well. There were fewer people, yes, but they also moved around a lot more. It's only comparatively recently that we've gotten stuck in our places and social structures.

What? I can't tell if this is a joke but the average person in the 1600s moved around a lot less than the average person today. I wouldn't be surprised if 80% of them never left a ten-mile radius.
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